An estimation device described in Patent Document 1 set forth below is known as a conventional estimation device for estimating an internal state, a parameter and the like of a battery.
This estimation device for estimating the parameter and the like of the battery detects a charging/discharging current and a terminal voltage of the battery and, based on inputs thereof, sequentially estimates the parameter and an open-circuit voltage with a Kalman filter by using a battery equivalent circuit model. A correction state of charge is estimated from the open-circuit voltage and, based on the correction state of charge, the charging/discharging current is corrected. A corrected charging/discharging current is integrated, and a value thus obtained is divided by a full charge capacity value. Thereby, a state of charge (SOC: State of Charge) of the battery is obtained more accurately.
Estimation of the parameter of the battery equivalent circuit model and the open-circuit voltage by the Kalman filter as described above so as to estimate the internal state of the battery such as the SOC and a state of health (SOH: State of Health) has been widely carried out by conventional techniques in addition to the Patent Document 1.
In this case, as disclosed in Non Patent Document 1 set forth below, for example, when a state equation and an output equation of a target system are affected by disturbance of white noise having a known covariance matrix, a gain matrix that minimizes a mean square state error may be selected. The Kalman filter is known as an observing device used for this purpose.
In other words, the Kalman filter may carry out an optimal prediction when it may be assumed that future values of the disturbance and the noise are equal to their mean values (i.e., zero).